1. Field of the Invention
The present invention relates to an electromagnetic wave generating devices for generating an electromagnetic wave such as an X-ray by electrons revolving in a circular orbit inside an accelerator
2. Description of the Prior Art
As conventional electromagnetic wave generating devices using annular accelerators, there have been devices that make use of an accelerator employing the principle of betatron acceleration (hereinafter refers to as “betatron accelerator”) Refer to Experimental Physics Lecture, Vol. 28 “Accelerator”, § 13 “Betatron”, pp. 547-563, edited by Kumagai Hiroo, published by KYORITSU SHUPPAN CO., LTD., Dec. 25 1975, ISBN: 4-320-03083-4 (Non-Patent Document).
A betatron accelerator is provided with an electromagnet to an accelerate electron beam emitted into a vacuum chamber by the magnetic field generated with alternating current flowing in exciting coils attached to the electromagnet. The accelerated electron beam impacts upon a metal target to emit an X-ray, which radiates outward from electromagnetic wave generating devices. The electromagnet has magnet pole portions and yoke portions to form magnetic circuits generated by the exciting coils. There have been varieties of the accelerators according to arrangements and combinations of the exciting coils, the magnet poles, and the yokes.
A conventional electromagnetic wave generating device using the betatron accelerator, for example, is configured with both magnet poles for focusing the electron beam and magnet poles for accelerating the electron beam on a common return yoke, or configured by combining the focusing magnet poles with the accelerating magnet poles each of which have been fabricated individually (e.g., refer to FIG. 13.2, p. 549 of the prior art). While, in this case, a focusing coil for exciting the focusing magnet poles and an accelerating coil for exciting the accelerating magnet poles may be used in common with each other, in cases where both incident electron beam and the X-ray emission need to be precisely controlled, respective electric power supplies for the focusing and accelerating coils are used independently.
Since the conventional electromagnetic wave generating device is so configured as described above, when the focusing and accelerating coils are provided independently in order to control the incident beam and the X-ray emission precisely, there have been problems as follows.
In cases of employing the common return yoke, the accelerating coil must be placed inside the focusing coil, which involves the accelerating coil to be placed inside a vacuum chamber, the power supply wires to the accelerating coil have no other choice but to be passed through between the vacuum chamber and the focusing magnet poles. Consequently, there have been problems in that reduction in the vacuum chamber volume causes electron beam loss to increase, or increase in the gap between the focusing magnet poles causes the focusing coil power supply and the electromagnet to increase in capacity and size, respectively.
Moreover, when the focusing and accelerating magnet poles are fully independent of each other, there has been a problem in that the accelerating magnet poles have to be made larger so that the electromagnetic wave generating device itself becomes bulky.